In direct contact steam injection heaters, steam is directly mixed into a flowing fluid (e.g. liquid or slurry) that is in the process of being heated. Direct contact steam injection heaters are well known in the art and are very effective at transferring heat energy to the flowing fluid. They provide rapid heat transfer with virtually no heat loss to the atmosphere, and also transfer both the latent and the available sensible heat of the steam to the liquid slurry.
Diffuser-type steam injection heaters are also known in the art. In the experience of this inventor, previous designs of diffuser-type steam injection heaters have utilized generally two-dimensional mixing strategies that tend to limit the steam flow to a small vertical spacing from the diffuser. As a result, there can be poor steam distribution throughout the fluid to be heated and subsequently “hot pockets” inside the pipe. In a highly viscous fluid, these hot pockets can lead to instability and “steam hammer.” This can also lead to damaging of the equipment, including the associated piping.
Another shortcoming of previous designs of diffuser-type steam injection heaters is that the plug that is carried within the diffuser typically utilizes a rotary, elastomeric, or otherwise pliant, seal design. In the experience of this inventor, such seals can quickly wear out as they ride over the holes that are contained within the diffuser. This occurs because the seals can “extrude” into and be damaged by the diffuser holes as the seals are repeatedly moved across the holes. Additionally, prior designs of diffuser-type steam injection heaters have used window-type openings in the plug and a rotary motion to control steam flow from the diffuser. In the experience of this inventor, such windows can lead to deformation in the plug when under pressure. Such deformation causes non-uniform gaps between the plug and the diffuser together with uneven and premature wear. It also causes premature plug failure.